Papillary thyroid cancer (PTC) is the thyroid gland's most common and treatable carcinoma, but new research has outlined a rare and much more serious variant of this disease.

A study published in the journal Thyroid analyzes 34 cases of diffuse sclerosing papillary thyroid cancer (DSPTC), which is evidently much more aggressive and resistant to treatment than typical PTC.

Common papillary carcinomas account for at least 70 percent of all cases of thyroid cancer diagnosed in the U.S., according to the Columbia University Department Surgery. However, PTC is a relatively mild form of the disease, and with treatment, it can be quite survivable.

An estimated 90 percent of individuals diagnosed with typical PTC will survive at least five years beyond initial treatment.

DSPTC, on the other hand, tends to spread farther and invade tissues faster. It is characterized by more extensive invasion of the lymph nodes, as well as by sclerosis, or hardening of the tissue. Researchers note that between 0.7 and 5.3 percent of PTC cases are DSPTC.

In the new study, scientists attempted to compile data from multiple reports of the rare sub-type in order to determine DSPTC's symptoms, presentation and optimal treatment.

By examining nearly three dozen recorded cases of the thyroid cancer variant, the study's authors established what they consider a solid clinical description the disease.

They noted that all but two patients with DSPTC presented with goiter prior to surgery but were otherwise experiencing normal thyroid function.

Patients with the diffuse sclerosing variation were much more likely to have a papillary thyroid tumor that encompassed both lobes of the gland, had multiple nodules and extended beyond the gland itself.

Metastasis in the lymph nodes indicated a high risk of recurrence of DSPTC, the researchers noted. Also, they found that the average age of diagnosis of the thyroid cancer variant was about 10 years younger than that of common PTC.

The team recommended that endocrinologists and clinicians be aware of DSPTC, since this variety of thyroid cancer entails a higher risk of metastasis and death than other, less aggressive forms of the disease.